In a real world deployment of a QKD system, it may not be cost effective to produce separate systems with different parameters for different operating conditions due to the additional effort and components required. An obvious issue is that Bob's basis choice is made using a fixed beam splitter. This means that \(P^B_X\)  will be fixed, unlike in the previous plots where we assumed one could choose any value. In contrast, as we explained in section REF , Alice's can easily vary her basis choice probability, \(P^A_X\) . In the remainder of the analysis we allow for \(P^A_X \ne P^B_X\) . We consider a long integration time of 30 minutes and \(QBER_I\)  of \(1\%\) . In models of fibre and satellite QKD systems, a value of \(0.5\%\)  has often been assumed [1]}, [2]}. The current value for \(QBER_I\)  is more conservative and reflects the fact that a mass produced commercial system may not be as well aligned as current experimental systems.
<FIGURE>